STATISTICAL OPTIMIZATION OF LEVAN FROM GLUCONOBACTER CERINUS BM11

Gluconobacter cerinus BM11 is an acetic acid bacterium isolated from Brazilian grapes that has demonstrated a great ability to produce levan with antioxidant properties. Levan is a polysaccharide that has attracted the attention due to a wide range of applications in food, cosmetic and pharmaceutical industry. Therefore, the aim of this study was to optimize the levan production by G. cerinus BM11 using the response surface methodology (RSM). Central composite rotatable design was used to study the main and the interactive effects of two factors on levan production: commercial sucrose and pH. Firstly, G. cerinus BM11 was cultivated in modified HS medium with different pH ranges (5.79 – 7.21) and containing different sucrose concentrations (13 % - 33 %; m/v). The incubation was maintained at 30 °C for 72 h under agitation (150 rpm). After, cells were removed by centrifugation and the supernatant was precipitated with cold ethanol. The formed precipitates were dissolved, hydrolyzed and levan was quantified as reducing sugars by Somogyi and Nelson method. Results showed that the maximum levan production (48.06 g/L) was obtained in HS medium supplemented with sucrose at 24.84 % (m/v) and initial pH of 6.95. Furthermore, the experimentally determined value agreed with predicted value (49.58 g/L). The statistical data exhibited a high significance of the regression and a high determination coefficient (R2) of 0.9868, indicating that 98.7% of the variation in the response could be explained by the model, as well as high value of the adjusted determination coefficient (R2adjust = 0.9735). Utilization of statistical design promoted a significant increase in levan production when compared to non-optimized conditions (13.89 g/L) thus facilitating its commercialization.